Edible oils can become rancid when exposed to oxygen. The challenge lies in stabilising these oils to increase their shelf life.
One way of achieving this is through hydrogenation. This involves chemically converting fatty acids to reduce the number of double bonds. In practical terms, hydrogenated oil is far more shelf-stable and will not go rancid as quickly as untreated oil. It also has a higher melting point, making it ideal for frying and pastry-making.